\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}\hat{\textbf{x}}_{k|k-1} = f(\textbf{x}_{k-1}, \textbf{u}_{k}, 0)\end{equation*}
\end{document}
